Underwater adhesives are specialized materials engineered to form strong bonds with surfaces while fully submerged in water. Unlike conventional glues that lose effectiveness in wet conditions, these substances overcome the challenges of aquatic environments. They enable repairs, construction, and various applications without removing objects from water. This innovative field addresses a long-standing limitation in material science.
Why Sticking Underwater is Difficult
Adhering materials underwater presents significant challenges due to water’s properties. Traditional adhesives rely on direct contact, but water molecules interfere by forming a layer between the adhesive and surface. This “interfacial water” prevents the adhesive from making intimate contact and establishing strong bonds.
Surface tension also plays a role, as water resists displacement, making it difficult for an adhesive to spread evenly. Contaminants in water, such as oils, particulates, or biological films, can further hinder adhesion. The curing process, which hardens the adhesive, is also complicated underwater, as water can interfere with these reactions or cause the adhesive to swell or degrade.
The Science Behind Underwater Adhesion
Underwater adhesives overcome wet environment challenges by employing specific principles. One mechanism involves displacing the water layer from the surface, allowing direct adhesive contact. Some adhesives are hydrophobic, repelling water to push molecules away from the bonding interface.
Once water is displaced, chemical bonding mechanisms activate. These include covalent bonds, involving electron sharing, or hydrogen bonds, which are weaker but numerous attractions. Many underwater adhesives also draw inspiration from marine organisms like mussels and sandcastle worms, which produce proteins that adhere strongly to wet surfaces. These bio-inspired adhesives often contain specialized sequences that form strong coordination complexes with surfaces.
Diverse Underwater Adhesives
A range of underwater adhesives have been developed, each with specific properties. Synthetic polymers are a broad category, often engineered to be highly hydrophobic or to cure effectively in water. Some synthetic glues incorporate catalysts and crosslinkers within microcapsules, which break upon application of force to initiate rapid solidification, even on untreated surfaces.
Bio-inspired adhesives represent another class, mimicking marine organisms. Mussels, for instance, produce proteins that stick firmly to submerged surfaces; researchers have replicated these proteins. Similarly, the sandcastle worm secretes a protein adhesive that spontaneously forms a water-immiscible fluid, enabling it to build durable underwater structures. Epoxies and polyurethanes are also formulated for wet environments, often modified to resist water degradation and provide robust bonding.
Where Underwater Adhesives Are Used
Underwater adhesives have utility across various sectors due to their ability to bond in wet conditions. In marine construction and repair, they fix ship hulls, maintain offshore oil and gas platforms, and repair submerged structures without costly dry-docking or dewatering. They offer a solution for patching leaks or reinforcing components in challenging underwater environments.
The medical field also benefits from these adhesives, particularly for surgical applications within the human body, which is inherently a wet environment. They are explored as alternatives to traditional sutures and staples for wound closure and tissue repair, offering potential for less invasive procedures and faster healing. Beyond these, underwater adhesives are employed in other areas, including repairing swimming pools and aquariums, sealing leaks in underwater pipelines and cables, and for recreational uses like patching inflatable boats or wetsuits.